The present invention relates to a cleaning method for a photoreceptor provided in image forming apparatus such as an electrostatic copying machine.
On the periphery of a photosensitive drum provided in image forming apparatus, the main charger, developing unit, image transfer device, separating device, cleaning device, etc. are disposed in that order in the direction of rotation.
The above-mentioned cleaning device is equipped with a cleaning means such as a cleaning blade or fur brush. Taking for example, the cleaning blade adopted for a copying machine having an image forming apparatus, the blade is so designed that it is turned on at the start of the copying action, comes in contact with the surface of the photosensitive drum so as to remove the residual toner from the surface of the drum and is turned off at the end of the copying action (see unexamined Patent Publication No. 46580/1985 for example).
However, when replacing a developing unit by another unit containing toner of a different colour to change the colour of copying and starting the copying action, it sometimes happens that the colour of the residual toner of a previous developing unit is mixed in a copied image. The cause of this kind of mixing of the colour of residual toner in the copied image is as follows. When the cleaning blade is turned off at the end of the copying action before the replacement of the developing unit, part of the residual toner accumulated at the upstream of the edge of the cleaning blade passes to the downstream side of the edge of the cleaning blade. Next, when starting copying operation by actuating the cleaning blade after replacing the developing unit, the residual toner at the downstream of the edge of the above-mentioned blade adheres to the photosensitive drum. This toner is then carried by the rotation of the drum to attach to a sealing member for protection against splashing provided at the top of the case of the developing unit. After that, this attached toner is adsorbed by an electrostatic latent image formed on the photosensitive drum and, as a result, transferred to the copying paper.
In the case of a cleaning device using a fur brush, the brush is made to come in contact with a photosensitive drum as it turns and the toner scraped down by the brush is exhausted by a fan. The part surrounding the fur brush is sealed with a sealing member. It sometimes occurs that the toner attaches to the downstream side face of the sealing member and, as a result, is mixed in the image as in the case of the replacement of the developing units mentioned above.
By such action, deterioration of the quality of the copied image occurs sometimes with the conventional type of multicolour developing unit when it is replaced by another unit of different colour, and an improvement in this respect has been strongly demanded.